Optical instruments such as endoscopes, borescopes, and exoscopes may include an electronic imaging device located, for example, at the distal end of an elongated shaft or in a camera head which is connected to an elongated shaft. Whether positioned at the distal end of the endoscope shaft or in the camera head, the electronic imaging device may be one or more charge coupled devices (CCDs) or CMOS imaging devices together with other electronic components. Other electronic devices such as LED or other light sources may be included in the instrument. The camera head (or an instrument body or handle in the case of some optical instruments) is typically connected via a suitable cable to a camera control unit, commonly referred to as a “CCU.”
The cable provides paths for carrying electrical power to the camera head and data signals to and from the camera head. In particular, image data captured by the imaging device is transmitted over the cable to the CCU for processing and ultimately for display on monitors which are connected directly to the CCU or to an intermediate device. Control signals and power for operating the electronic components in the instrument may be transmitted over the cable from the CCU to the scope and/or camera head.
An endoscope 2, as illustrated in FIG. 1, usually includes a first imaging lens (e.g., an objective) followed by a series of carrier lenses (e.g., relays) which capture and transmit an optical image from inside an enclosed area 1 to the outside. The proximal end of the endoscope 2 may be attached, via direct coupling or an adaptor, to a camera head 3 or an eye-piece for viewing. The camera head 3 usually includes lenses for receiving the optical image and forming a real optical image onto the image sensor. The digital image captured by the image sensor can then be transmitted to a CCU or other similar modules for analysis and display.
Endoscopic imaging is difficult due to limitations of form factor, propagation losses, and the wide range of distances at which objects are observed with an endoscope. The small diameter of the light carrier and corresponding light beam also makes zooming and focusing particularly difficult. Because of the small diameter, most conventional lens actuators require too much radial space to be used. However, some liquid lenses can fill the light channel and can vary without movement.
The endoscope lens in Pauker, et al. (U.S. Pat. No. 7,889,434) includes a number of lens units where each lens can be individually reshaped by hydraulic pressure to change the focal length of each one. Each lens is a liquid lens containing a compressible liquid or gas so that when pressure is introduced to the gaps between the lenses the optical power of the lens changes. This method enables a set of fixed liquid lenses to focus and zoom.
Pauker also discloses varying the position of several solid lenses by varying the pressure of a medium disposed in sealed chambers in between each lens of the lens cylinder. These pressure variations push the lenses closer of farther apart, changing the focal length of the lens unit. Both the methods of variable focus in Pauker, however, require complicated hydraulics, specialized fluids and sealed chambers which are difficult to manufacture and use.
A number of different lens systems are disclosed in Bueler, et al (US 2010/0231783) which have varifocal deformable lenses along with solid lenses in various arrangements, the entire disclosure of which is incorporated herein by reference. Some of the varifocal zoom lenses simply change in optical power while others can flip between positive and negative optical power allowing the lens to focus or expand the light beam.
In addition, Bueler discloses several varifocal and deformable lenses which are used in either the zoom lens or the focal lens, or both. Both the deformable zoom lens and deformable focal lens are constructed of a membrane with a deformable portion and a filler material. The deformable portion can be tuned at least in part by an electrostatic actuator, an electromagnetic actuator, a piezo-motor, a magneto-strictive actuator, a stepper motor, or an electroactive polymer actuator for a high focus tuning range.
Kuiper, et al. (US 2011/0118610) discloses an endoscope with a zoom lens and a movable image sensor, where the zoom lens is a liquid zoom lens with no membrane in between two immiscible liquids. This allows for manipulation of the curvatures of the two different liquids to change the optical power of the lens. To offset the resulting change in focal plane, the image sensor is moved to the correct location. Thus, in this setup, no focal lens is needed downstream of the zoom lens.
However, the prior art devices use deformable lenses instead of moveable lenses due to the limitations of the form factor of an endoscope. The small diameter of the endoscope requires small lenses to be used. In the prior art, if solid moveable lenses are used to zoom or focus, they require actuators along their outside edges which require additional radial space.
Thus, in order for conventional systems to use moving lenses, these lenses must be even smaller. The listed prior art above describes these limitations as necessitating the replacement of the smaller moving lenses with liquid deformable lenses. These liquid lenses have several disadvantages including the need for specialized actuators for displacing fluid, low durability and resilience, and higher optical imperfections like variable astigmatisms which cannot be corrected. They are also difficult to manufacture and use.